From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757211AbeDXLy4 (ORCPT ); Tue, 24 Apr 2018 07:54:56 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:36934 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751436AbeDXLym (ORCPT ); Tue, 24 Apr 2018 07:54:42 -0400 X-Google-Smtp-Source: AB8JxZocqvnOGnzPycMMEsgneqyAM9kqY/AJXva4Hqk0iDQez3cXKkFZilgblBMAnzA0KnxQ7bgVJg== Date: Tue, 24 Apr 2018 13:54:37 +0200 From: Daniel Vetter To: Oleksandr Andrushchenko Cc: Wei Liu , jgross@suse.com, Artem Mygaiev , Dongwon Kim , konrad.wilk@oracle.com, airlied@linux.ie, "Oleksandr_Andrushchenko@epam.com" , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, "Potrola, MateuszX" , daniel.vetter@intel.com, xen-devel@lists.xenproject.org, boris.ostrovsky@oracle.com, Roger Pau =?iso-8859-1?Q?Monn=E9?= Subject: Re: [Xen-devel] [PATCH 0/1] drm/xen-zcopy: Add Xen zero-copy helper DRM driver Message-ID: <20180424115437.GT31310@phenom.ffwll.local> Mail-Followup-To: Oleksandr Andrushchenko , Wei Liu , jgross@suse.com, Artem Mygaiev , Dongwon Kim , konrad.wilk@oracle.com, airlied@linux.ie, "Oleksandr_Andrushchenko@epam.com" , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, "Potrola, MateuszX" , daniel.vetter@intel.com, xen-devel@lists.xenproject.org, boris.ostrovsky@oracle.com, Roger Pau =?iso-8859-1?Q?Monn=E9?= References: <20180417075928.GT31310@phenom.ffwll.local> <20180417205744.GA15930@downor-Z87X-UD5H> <41487acb-a67a-8933-d0c3-702c19b0938e@gmail.com> <20180418073508.ptvntwedczpvl7bx@MacBook-Pro-de-Roger.local> <20180418101058.hyqk3gr3b2ibxswu@MacBook-Pro-de-Roger.local> <20180420071914.GG31310@phenom.ffwll.local> <76cdc65a-7bb1-9377-7bc5-6164e32f7b5d@gmail.com> <20180423115242.ywdwqblj2aseu3fr@citrix.com> <61105351-8896-072b-abf0-757c7f6c0edf@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <61105351-8896-072b-abf0-757c7f6c0edf@gmail.com> X-Operating-System: Linux phenom 4.15.0-1-amd64 User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 23, 2018 at 03:10:35PM +0300, Oleksandr Andrushchenko wrote: > On 04/23/2018 02:52 PM, Wei Liu wrote: > > On Fri, Apr 20, 2018 at 02:25:20PM +0300, Oleksandr Andrushchenko wrote: > > > > > the gntdev. > > > > > > > > > > I think this is generic enough that it could be implemented by a > > > > > device not tied to Xen. AFAICT the hyper_dma guys also wanted > > > > > something similar to this. > > > > You can't just wrap random userspace memory into a dma-buf. We've just had > > > > this discussion with kvm/qemu folks, who proposed just that, and after a > > > > bit of discussion they'll now try to have a driver which just wraps a > > > > memfd into a dma-buf. > > > So, we have to decide either we introduce a new driver > > > (say, under drivers/xen/xen-dma-buf) or extend the existing > > > gntdev/balloon to support dma-buf use-cases. > > > > > > Can anybody from Xen community express their preference here? > > > > > Oleksandr talked to me on IRC about this, he said a few IOCTLs need to > > be added to either existing drivers or a new driver. > > > > I went through this thread twice and skimmed through the relevant > > documents, but I couldn't see any obvious pros and cons for either > > approach. So I don't really have an opinion on this. > > > > But, assuming if implemented in existing drivers, those IOCTLs need to > > be added to different drivers, which means userspace program needs to > > write more code and get more handles, it would be slightly better to > > implement a new driver from that perspective. > If gntdev/balloon extension is still considered: > > All the IOCTLs will be in gntdev driver (in current xen-zcopy terminology): >  - DRM_ICOTL_XEN_ZCOPY_DUMB_FROM_REFS >  - DRM_IOCTL_XEN_ZCOPY_DUMB_TO_REFS >  - DRM_IOCTL_XEN_ZCOPY_DUMB_WAIT_FREE s/DUMB/DMA_BUF/ please. This is generic dma-buf, it has nothing to do with the dumb scanout buffer support in the drm/gfx subsystem. This here can be used for any zcopy sharing among guests (as long as your endpoints understands dma-buf, which most relevant drivers do). -Daniel > > Balloon driver extension, which is needed for contiguous/DMA > buffers, will be to provide new *kernel API*, no UAPI is needed. > > > Wei. > Thank you, > Oleksandr > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch